The present invention relates to a polycaprolactam composition having an improved melt spinnability.
When polycaprolactam is melt-spun for a long time, thermal degradation or decomposition products such as tar are deposited and accumulated on the edge of a spinneret nozzle. This tar causes a so-called "bending" phenomenon in which an extruded molten polymer is bent in a direction different from the yarn take-up direction, resulting in enhancement of unevenness in the resulting yarn and increase of yarn breakages. This tar product is formed according to the following mechanism. Namely, a monomer (.epsilon.-caprolactam), oligomers or a thermal decomposition product of the polymer present in molten polycaprolactam volatilizes or sublimates during melt spinning and is oxidized on the surface of a spinneret.
As means for preventing formation of this tar product, Japanese Patent Publication No. 30007/69 discloses a process in which various additives, for example, organic tin compounds such as tetra-amyl tin and tetrabenzyl tin, are incorporated in polycaprolactam. Further, U.S. Pat. No. 3,907,743 teaches a method in which 0.001 to 0.05% by weight of Mg(CH.sub.3 COO).sub.2, MgCl.sub.2, MgBr.sub.2 or Mg(NO.sub.3).sub.2 and 0.05 to 5% by weight o an organic tin compound are incorporated in a polyamide and the resulting composition is melt-spun, thereby to reduce build-up of carbonized materials on the surface of a spinneret during spinning of a synthetic linear polyamide.
Most of these known additives are still insufficient in the effect of preventing accumulation of tar or carbonized materials and thus preventing occurrence of the bending phenomenon, and even if some of them are effective, they are poisonous. Moreover, incorporation of these additive often results in degradation of properties of polycaprolactam. Therefore, various difficulties should be overcome in order to put these additives into practical use.